The aim of this experiment is to investigate the relationship between the current, voltage and resistance through the use of a fixed resistor and a filament lamp.

Extracts from this document...

Introduction

Abdul Mufti Centre Number: 13329 Candidate Number: 4138

10. F

Aim

The aim of this experiment is to investigate the relationship between the current, voltage and resistance through the use of a fixed resistor and a filament lamp.

Hypothesis

Based on knowledge of Ohm’s law it can be hypothesised that when an increasing voltage and current is passed through a filament lamp the resistance would increase in an irregular fashion, so that a graph similar to the one given below would be seen (figure 1). This curved graph would be expected due to temperature increases in the filament lamp.

It can also be hypothesised that when current is passed through a fixed resistor a straight line graph would be obtained (figure 2) this is explained in figure 3.

Circuit Diagrams

Equipment

Fixed resistor &

Filament Lamp– to impede and obstruct current flowing through circuit

Ammeter– to measure current flowing through the circuit

Voltmeter– to measure the voltage present in the circuit and to make sure the power supply is correctly calibrated.

Power Supply– to act as the adjustable power source for the circuit

Wires–to connect the circuit components. Tangles were removed from the wires as not doing so could result in erroneous values being obtained in the experiment, as using several different wires or tangled wires during the experiment could lead to varied resistance and poor fair test (Figure 6).

The equipment was then turned on. As the voltage on the PSU was increased it was confirmed on the voltmeter and the reading on the ammeter was noted. For the first circuit a total of 7 ammeter readings were taken and repeated. Each time the voltage was increased by 2 V.

The value for each voltage was recorded in the table. Once the highest voltage had been reached for the PSU the circuit was switched off and the fixed resistor was replaced with a filament lamp (figure 6). The voltage readings were then repeated as before and were inserted in another table. After this the equipment was cleared away. The tables were then plotted onto graphs.

Method in summary:

Apply safety precautions.

Gather equipment and connect it according to figure 4.

Recheck for safety and turn the circuit on.

Increase the Voltage by 2V every reading and note the current reading on the ammeter.

Once 12V is reached switch the PSU off.

Replace resistor with a Filament Lamp

Carry out steps 3-5 again.

Once readings for filament lamp and fixed resistor are tabulated clear up equipment.

Plot an I-V graph for the fixed resistor and Filament Lamp.

Variables

The controlled variables in this experiment are the resistors and equipment used.

To conduct a fair test it would have been practical to use averages for a series of current readings. This could be done by using two different sets of equipment, conducting the experiment on each set and averaging the values. This could help us reduce the margin of error in any anomalies found. It may have been interesting to investigate the same aim with a wider range and more sensitive set of equipment. Smaller increases of voltage on the PSU would have allowed us to plot the graphs with more accuracy. If possible it would have been interesting to use a diode. We may also have adjusted variables such as the thickness, length and type of wire used to investigate the effect these factors have on Ohm’s law and our graphs. we would also investigate how changing the circuit diagram would have affected our results.

Related AS and A Level Electrical & Thermal Physics essays

Though small, these losses are of great economic and practical importance; all the electricity generated in a power station is transformed several times before it is put to use. If the losses at each transformer were 1%, it would result in 4 or 5% of all electricity production being wasted as heat in transformers.

The filament lamp can become very hot so make sure that you do not burn yourself on it. Make sure none of the equiptment is faulty. Conclusion In conclusion the results graph proves that a filament bulb does not obey Ohm's law as the gradient changes in steepness and curves horizontally.

Plan For this experiment, I will have one independent variable. This is going to be the voltage. As the voltage of the circuit is going to vary, there will be at least two dependant variables. These are going to be the current flowing through the circuit, and for the bulb

We know that Voltage is directly proportional to the current and Resistance is inverse proportional to current. I? V I ? 1 If we combine these two equations together we get I=V/R, if we re-arrange this formula we get ohm's law V=I.R.

The results should then be presented graphically, as the outcome of the line will show the relationship between the current and voltage. A straight line will show the component does obey ohms law as the current is constant and proportional to the p.d.

I also made sure that I carried out the experiment in a safe way and abiding by the safety precautions mentioned in the planning phase. The Results are on the next page... The Results: The first set of results is shown in the table below: Constantan wire (diameter of 0.11mm)